The effectiveness of an intravenously injected ultrasound contrast agent (Levovist) to enhance Doppler signals from within and around breast masses will be evaluated. The procedure will be videotaped using a standard protocol, allowing for independent reading as well as intra- and inter- observer reliability measurements. Doppler pulsatility and resistive indices will be recorded as well as the peak systolic frequency and the minimum end diastolic frequency. The region of the breast mass will be examined with color and pulsed Doppler ultrasound, recording arc of vascularity within and around the visualiied mass. A dose of the ultrasound contrast agent will then be injected intravenously as a series of Doppler ultrasound recordings are taken from the mass and/or the adjacent normal portion of the breast. Since the agent lasts for up to six minutes, it will be possible to obtain information in both color and pulsed form, in both the normal and tumor regions. Contrast enhanced color harmonic imaging will also be performed. Specifically, the differences between the time of peak contrast enhancement and the washout of the contrast agent in benign and malignant masses will be measured. The hypothesis is that an ultrasound contrast agent will improve the ability to detect and differentiate tumors compared to images by x-ray mammography, conventional ultrasound and non-enhanced color Doppler. Surgical and pathological results will be used as a gold standard.